An influential scientific panel is meeting on Tuesday to discuss who should receive a newly authorized Covid-19 vaccine from Novavax, a Maryland pharmaceutical company that hopes its shot will appeal to Americans who have so far declined to be vaccinated.The independent experts, who advise the Centers for Disease Control and Prevention on its vaccine policies, will convene at 10 a.m. Eastern (you can watch the meeting here). They are scheduled to vote on whether to endorse Novavax’s latecomer vaccine, which is expected to play a limited role in the country’s immunization campaign, at least initially. The Food and Drug Administration last week authorized it as a primary immunization for adults, but has not yet considered it for a booster shot.The Biden administration said last week that it would buy 3.2 million doses of the two-shot vaccine, enough to fully vaccinate 1.6 million people in the United States. The vaccine is not yet available in pharmacies and other clinics that administer shots in the United States. In announcing the purchase, the government said that Novavax was expected to soon finish its quality testing, a necessary step before the doses can be released.If the C.D.C. panel, called the Advisory Committee on Immunization Practices, votes to endorse the vaccine’s use, the next step will be for the C.D.C. director, Dr. Rochelle Walensky, to accept its recommendations, which typically happens swiftly.The vaccine was found to be highly protective against infection and severe disease from the coronavirus in clinical trials, but those were conducted before the emergence of the Omicron variant, which has sharply reduced the effectiveness of other authorized vaccines in preventing infections.At the meeting on Tuesday, a C.D.C. official will review clinical trial data that has linked the vaccine to an elevated but small risk of developing forms of heart inflammation known as myocarditis and pericarditis. In their review of Novavax’s data, F.D.A. scientists identified six cases of the conditions in about 40,000 trial volunteers.Novavax’s vaccine works differently from the three Covid vaccines previously authorized in the United States. It provokes an immune response with nanoparticles made up of proteins from the surface of the coronavirus that causes Covid-19. Similar protein-based vaccines have been used globally for decades.Novavax executives contend that this tried-and-true technology will make the vaccine more acceptable to those concerned that the messenger RNA technology used by Pfizer-BioNTech and Moderna in their vaccines, which account for the vast majority of the vaccinations in the United States.

The Food and Drug Administration on Wednesday authorized a Covid-19 vaccine developed by Novavax, a biotechnology company in Maryland that received significant federal funding to produce the shot. The vaccine will be a new option for Americans as vaccination rates stagnate.After two years of development, the vaccine has finally overcome manufacturing problems to become the fourth shot to earn clearance in the United States. Advisers to the Centers for Disease Control and Prevention will meet next week and are expected to discuss who should get the Novavax vaccine.The two-dose vaccine was authorized as a primary immunization series for adults, rather than a booster, which is likely to limit its market at first. The Biden administration said earlier this week that it would buy 3.2 million doses, enough to fully vaccinate 1.6 million people in the United States. In announcing its purchase, the government said that Novavax was expected to finish its quality testing “in the next few weeks,” a necessary step before the doses are released.Novavax hopes that its vaccine will appeal to people who have spurned the shots from Pfizer-BioNTech and Moderna, which use messenger RNA technology. About 22 percent of people in the United States have not received a single Covid vaccine dose.Novavax’s vaccine, given in doses spread three weeks apart, works differently from mRNA vaccines. It provokes an immune response with nanoparticles made up of proteins from the surface of the coronavirus that causes Covid-19. Similar protein-based vaccines have been widely used around the world for decades.But modest demand for the Novavax shot in other wealthy countries leaves it unclear if the company’s prediction for the United States will hold up. In Europe, only 12.6 million Novavax doses were distributed between December, when the vaccine was authorized there, and June 30. In contrast, more than a billion doses of Pfizer-BioNTech and Moderna vaccines have been distributed in Europe.A Morning Consult poll released earlier this month suggests that Novavax may meet a similar lack of enthusiasm in the United States. Only 10 percent of unvaccinated people contacted for the poll said they would definitely or probably get a protein-based vaccine.The authorization comes with a warning that Novavax’s vaccine is linked to an elevated but small risk of forms of heart inflammation known as myocarditis and pericarditis. In their review of Novavax’s data, F.D.A. scientists identified six cases of the side effect in about 40,000 trial volunteers.The mRNA vaccines from Moderna and Pfizer-BioNTech are also linked to an elevated risk of these conditions, but that link did not emerge until after they were put into large-scale use. A warning about the risk was also added to their packaging.Before the pandemic, Novavax was a little-known biotechnology company with several vaccines in the research pipeline, but no approved products. It rose to prominence when Operation Warp Speed, the federal government’s 2020 campaign to develop coronavirus vaccines, picked it out for support. The program initially agreed to pay up to $1.6 billion to fund the development of the vaccine and to purchase up to 100 million doses of the shot.But a series of manufacturing delays meant that the shot was not available for the initial surge of vaccinations in the United States in early 2021.The manufacturing woes have continued to dog the company. Even after an F.D.A. advisory committee recommended authorizing the vaccine in early June, the agency took weeks to give it the green light, because it needed more time to sign off on Novavax’s manufacturing process. The Serum Institute of India, the world’s largest vaccine producer, is manufacturing Novavax’s vaccine.In a number of clinical trials, Novavax found that its vaccine was highly protective against symptomatic infection. But the original formulation is probably not as effective against the Omicron variant, which emerged in November and has evaded some of the protection afforded by authorized vaccines from other companies.Novavax is developing new versions of its vaccine that target Omicron and its highly contagious subvariants. Preliminary data from laboratory and animal studies indicate that a booster shot aimed at a previous Omicron subvariant, BA.1, generates strong immune responses to the virus. The company says it expects to have results from a clinical trial of that shot in September, with doses ready in the last three months of this year.The company says it plans to accelerate its research on shots specifically tailored for two newer versions of Omicron, known as BA.4 and BA.5.Trials have also shown that Novavax’s shot works well as a booster, and the company is expected to seek authorization for boosters soon. The company may then be able to attract vaccinated people who want to switch to a new option to protect against new variants.John Moore, a virologist at Weill Cornell, said he considered Novavax an excellent vaccine but was not yet convinced that an Omicron-based booster would provide much extra protection compared with the original version. “There’s too little information,” he said.Dr. Moore speculated that some people might switch to Novavax for a booster this fall because it produced relatively few cases of aches, fatigue and other passing side effects in clinical trials. That was his experience as a volunteer in one of Novavax’s trials. “The only way I could tell the next day which arm I had the needle in was the Band-Aid,” he said.If Novavax is authorized for a booster, Dr. Moore would happily return for another shot, he said: “At some point in the fall, I’ll have another dose, and it would be Novavax.”

The F.D.A. said the drug should be prescribed mainly when other treatments were “not accessible or clinically appropriate.”The Food and Drug Administration on Thursday authorized a second antiviral pill for Covid but said it should not be preferred over other treatments.The F.D.A. cleared the pill, developed by Merck and known as molnupiravir, for adults who are vulnerable to becoming severely ill from Covid and for whom alternative treatment options are “not accessible or clinically appropriate.”The agency’s decision reflects concerns that Merck’s pill is only modestly effective and carries possible safety risks, including for pregnant women.Merck’s treatment is expected to be available early next month. With the Omicron variant driving an onslaught of infections, the drug will be in greater supply in the coming weeks than other treatments in the United States.Older people and those who have conditions like obesity, diabetes or heart disease would be eligible to get a prescription for Merck’s pills if they become sick from the coronavirus and cannot get treatments like Pfizer’s newly authorized pills or monoclonal antibody drugs. Both vaccinated and unvaccinated people will be eligible.But while the agency authorized Pfizer’s treatment for high-risk Covid patients as young as 12, it said that it was authorizing Merck’s drug only for adults because it “may affect bone and cartilage growth.”Even before the F.D.A.’s decision, some doctors and health officials had tempered expectations for Merck’s drug. It appears far less effective than a similar pill from Pfizer, which received F.D.A. authorization on Wednesday and is expected to become more widely available in the United States starting in a few months.In a key clinical trial, Merck’s drug reduced the risk of hospitalization or death by 30 percent when given to high-risk, unvaccinated people within five days of the onset of symptoms. Pfizer’s pill was found to reduce that risk by 88 percent.“I don’t think Merck’s version is going to be the game changer,” said Dr. Walid Gellad, who directs the Center for Pharmaceutical Policy and Prescribing at the University of Pittsburgh.Dr. Dean Li, a Merck executive, said on Thursday that preliminary laboratory studies suggested that the drug was equally effective against Omicron as it was against earlier versions of the virus. The company and independent researchers have been running experiments on how well the drug can stop the Omicron variant from replicating.The pills from Merck and Pfizer can be taken at home and are expected to reach many more people globally than monoclonal antibody treatments, which are typically given via intravenous infusions by a health care provider.Until this week, the antibody drugs have been the only authorized treatment option for Covid patients who are at high risk of becoming severely ill. But Omicron has wreaked havoc on the country’s supply of the antibodies.On Thursday, the federal government paused distribution of the treatments from Regeneron and Eli Lilly, saying it was unlikely they would work against Omicron. Those treatments represented nearly all of the country’s supply. The only antibody treatment that remains potent against the new variant, from GlaxoSmithKline and Vir Biotechnology, is in very limited supply for now.In that context, the value of Merck’s pill has increased, experts said.“Anything that keeps people out of the hospital, even incremental, has a role,” said Dr. Nahid Bhadelia, director of the Center for Emerging Infectious Diseases Policy and Research at Boston University.In early November, the Delta variant started fueling a rise in coronavirus cases, particularly in the Midwest and the Northeast. Omicron, which rapidly became the dominant form of new cases in the United States, is now driving the surge.Merck’s treatment is meant to be taken as 40 pills over five days. The company is ready to ship the first 378,000 courses for the United States within days. Merck is expected to fulfill the federal government’s full order of enough pills for 3.1 million people, at a cost of about $700 a person, by the end of January.Pfizer is expected to provide enough of its pills, known as Paxlovid, for 265,000 Americans before the end of January. The federal government on Thursday allocated the first 65,000 treatment courses to states and said the first shipments would begin arriving within the next few days.As was done with Covid vaccines, the federal government will allocate the pills to states, which can then distribute them to health departments and pharmacies. The government will also ship the pills directly to community health centers.The Coronavirus Pandemic: Key Things to KnowCard 1 of 5The holiday season.

The first-of-its-kind treatment, Paxlovid, has been found to be highly protective against severe illness. It could be available within a few days.The Food and Drug Administration on Wednesday authorized the first pill for Covid-19, offering a highly effective defense against severe illness that will arrive as the country endures another major surge of the pandemic.The drug, developed by Pfizer and known as Paxlovid, is authorized for Covid patients age 12 and over who are vulnerable to becoming severely ill because they are older or have medical conditions such as obesity or diabetes. Tens of millions of Americans — including both vaccinated and unvaccinated people — will be eligible if they get infected with the virus. The treatment could be available within a few days.Pfizer’s laboratory studies indicate that its pills are likely to work against the Omicron variant, which has rapidly become the dominant form of new cases in the United States.A clinical trial indicated that Paxlovid is highly effective when taken soon after people start feeling sick. In a final analysis of a key study conducted while the Delta variant was surging, Pfizer’s drug reduced the risk of hospitalization or death by 88 percent when given to high-risk unvaccinated adults within five days of the start of their symptoms.Paxlovid appears to be substantially more effective than a similar antiviral pill from Merck, known as molnupiravir, that is still awaiting authorization by the F.D.A. In a clinical trial, Merck’s drug reduced risk of hospitalization and death for high-risk patients by 30 percent.Until now, monoclonal antibody drugs, which are typically infused into the bloodstream at a hospital or clinic, have been the only authorized treatments for Covid patients who are not hospitalized but at higher risk of developing severe disease. But the antibodies have gone to fewer people than the pills are expected to reach, and most of the country’s supply of the antibody treatments is unlikely to work against Omicron.The federal government has ordered enough of Pfizer’s pills to cover 10 million people, at a cost of about $530 per patient, but the supply will be limited at first.Within a week, Pfizer is expected to make available to the United States enough of its pills to cover 65,000 Americans. At current infection rates, that would be enough supply for less than one day if it were given to half of people in the United States who test positive for the virus.Pfizer is expected to make available to the United States another 200,000 treatment courses in January. The pace of deliveries is expected to increase sharply in the subsequent months, with Pfizer expected to fulfill the government’s full order by late summer.Coronavirus cases have been increasing since early November, particularly in the Midwest and Northeast, driven first by the Delta variant and now mostly by Omicron.The federal government will allocate the antiviral pills to states, which can then distribute them to local health departments and pharmacies, as was done with Covid vaccines. The government will also distribute the pills directly to community health centers.“The tough thing for states to figure out is who to make it available to, since there’s so few to begin with,” said Dr. Nahid Bhadelia, director of the Center for Emerging Infectious Diseases Policy and Research at Boston University. “You want to make sure that it’s at least given to people who are the most likely to benefit from it.”She said it would be important for state and local governments to prioritize getting the pills to medically vulnerable people, particularly in nursing homes and clinics in hard-hit communities.To get Pfizer’s pills, the F.D.A. said, patients will need to test positive for the virus and get a prescription from a health care provider, all within no more than five days after their symptoms start. Those requirements may pose serious challenges.While the agency did not specify which type of test will be needed, over-the-counter rapid antigen tests, which return results within 15 minutes, are expected to be widely used. President Biden announced on Tuesday that the administration is buying 500 million rapid tests to distribute free to the public, but it is not clear if that will be enough to meet what is expected to be very high demand.There is also a risk that Americans most in need of the pills will refuse them, just as they have spurned vaccines. About half of unvaccinated adults polled by Morning Consult said they would not take F.D.A.-authorized antiviral pills if they got sick with Covid.Pfizer expects to produce 120 million courses of Paxlovid in 2022. The company already has deals to sell its pills to a number of wealthy countries, and says it’s in discussions with dozens of governments around the world about additional supply deals. It has also agreed to allow other manufacturers to inexpensively make and sell the pills to poorer countries.The Coronavirus Pandemic: Key Things to KnowCard 1 of 5The holiday season.

As the world reels from the emergence of the Omicron variant of the coronavirus, a panel of advisers to the Food and Drug Administration will meet on Tuesday to discuss an antiviral pill from Merck, the first in a new class of treatments that could work against a wide range of variants.The expert committee will vote on whether to recommend authorizing the drug, known as molnupiravir, for high-risk patients. The treatment — which has been shown to modestly reduce the risk of hospitalization and death, predominantly from the Delta, Mu and Gamma variants — could be authorized in the United States within days, and available soon after, if the committee endorses the drug and the agency follows the recommendation. The panel’s meeting on Tuesday is scheduled to begin at 9 a.m. Eastern time and can be watched here.In the coming weeks, the F.D.A. may also greenlight a similar pill from Pfizer that appears to be significantly more effective than Merck’s.Health officials around the world have been counting on the new treatments to reduce the number of severe cases and save lives. If Omicron causes a surge in severe infections, it could make them even more important.Scientists have yet to run experiments to see how well the pills block Omicron viruses from replicating. But there are reasons to think they would remain effective even if the variant can sometimes evade vaccines.Omicron has more than 30 mutations on the so-called spike protein that latches on to human cells. Some of those mutations may make it hard for vaccine-produced antibodies to attack the virus.But the pills do not target the spike protein. Instead, they weaken two proteins involved in the virus’s replication machinery. Omicron carries only one mutation in each of those proteins, and neither looks as if it would stop the pills from doing their jobs.Virus cases are rising in many regions of the United States, notably the Upper Midwest and Northeast. Nationwide, cases have risen since the start of November, raising fears about a winter surge fueled by the Omicron variant, indoor holiday gatherings and the refusal of tens of millions of Americans to be vaccinated.In a clinical trial, molnupiravir was found to reduce by 30 percent the risk of hospitalization or death when given to high-risk, unvaccinated volunteers within five days after they started showing symptoms. It appears to be substantially less effective than Pfizer’s pill, which was found to lower risk by 89 percent, and monoclonal antibody treatments, which have been found to cut it by at least 70 percent.If molnupiravir is authorized in the United States, supply is expected to be limited at first, though it will be more abundant than Pfizer’s pill. The Biden administration has ordered enough courses of treatment, at about $700 per person, for 3.1 million people. Merck is expected to supply those pills before February.The Coronavirus Pandemic: Key Things to KnowCard 1 of 4The Omicron variant.